surface mirror (float samples = 1,
                      samplecone = 0)
{
/* STEP 1
        Make a copy of the surface normal one unit in length */
vector  i = normalize(I);
normal  n = normalize(N);
 
/* STEP 2
        Nothing fancy with the apparent opacity */
Oi = Os;
 
/* STEP 3
        Only raytrace reflections from the front surface */
if(n.-i >= 0)
    {
    vector  reflectRay = reflect(i, n);
    color   gatherColor = 0,hitc = 0;
    float   numhits = 0;
 
    gather("illuminance", P, reflectRay, 
       samplecone * PI/180, samples, "surface:Ci", hitc) 
        {
        gatherColor += hitc;
        numhits += 1;
        }
    /* Find the average color */
    gatherColor /= numhits;
    Ci = gatherColor * Cs * Oi;
    }
else
    Ci = Cs * Oi;
}